Computing devices, such as notebook computers, personal data assistants (PDAs), mobile communication devices, portable entertainment devices (such as handheld video game devices, multimedia players, and the like) and set-top-boxes (such as digital cable boxes, digital video disc (DVD) players, and the like) have user interface devices, which are also known as human interface devices (HID), that facilitate interaction between the user and the computing device. One type of user interface device that has become more common is a touch-sensor device that operates by way of capacitance sensing. A touch-sensor device usually is in the form of a touch-sensor pad, a touch-sensor slider, or touch-sensor buttons, and includes an array of one or more capacitive sense elements. The capacitance detected by a capacitance sensor changes when a touch object makes contact with the sensor. The touch object can be, for example, a stylus or a user's finger.
One type of capacitance sensing device includes multiple touch sense electrodes arranged in rows and columns and forming an array of intersections. At each intersection of the electrodes in the X and Y dimensions (i.e., a location where the approximately orthogonal electrodes cross over, but do not connect with, one another), a mutual capacitance is formed between the electrodes thus forming a matrix of capacitive sense elements. This mutual capacitance is measured by a processing system and any change in capacitance (e.g., due to the contact or movement of a touch object) can be detected. In a touch-sensor device, a change in capacitance detected by each sense element in the X and Y dimensions of the sense array can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance detected by the capacitive sense elements is processed by a processing device, which in turn produces electrical or optical signals representative of the position of the touch object in relation to the touch-sensor pad in the X and Y dimensions. A touch-sensor strip, slider, or button operates on the same capacitance-sensing principle.
Certain computing devices may also process user input based on the proximity of an object to the device, rather than actual touch. For example, the touch-screen of a mobile phone may be deactivated when it is placed near a user's face to prevent touch-input commands from being entered due to inadvertent contact. Additionally, other computing devices may recognize gestures performed with the user's hand when it is near the computing device. For example, swiping a hand near the screen of an electronic reader may turn the page of an e-book either forwards or backwards. These proximity controls and gestures may be implemented using infrared (IR) technology. The computing device may include an IR transmitter which emits an IR signal. When an object (e.g., the user's hand) is near the device, some portion of the IR signal may be reflected back to the device and detected by an IR receiver. A processing device interprets the received signal to determine the presence and/or position of an object. The device can then perform an appropriate action based on the proximity or gesture detected. This technique, however, makes use of a dedicated IR sensor and associated chips for processing. At least four IR sensors would be used to detect even the simplest gestures. This may increase the overall cost of the computing device. In addition, the IR sensors may be sensitive to external IR fields, which could lead to saturation and negatively affect operation of the device.